RESUMO
Exoinulinase (beta-d-fructan fructohydrolase, EC 3.2.1.80) secreted by Aspergillus terreus CCT4083 was obtained using sugar cane bagasse, an agroindustrial residue, as a carbon source. It was further purified from the supernatant culture in a rapid procedure. The enzyme presented 57 kDa on SDS-PAGE and 56 kDa on gel filtration chromatography. Inulin was hydrolyzed by the purified enzyme, yielding d-fructose as the main product. This enzyme showed maximum activity at pH 4.0 and 60 degrees C and maintained more than 90 and 75% of its original activity at 40 and 50 degrees C, respectively, after 3.5 h of preincubation. The K(M) values for inulin, sucrose, and raffinose were 11, 4.20, and 27.89 mM, respectively, and d-fructose was a competitive inhibitor (K(i) = 47.55 mM). The activation energies for sucrose, raffinose, and inulin were 10.4, 5.61, and 4.44 kcal/mol, respectively. The characteristics of A. terreus exoinulinase were compared to those of inulinases isolated from other organisms. The exoinulinase traits presented especially good thermostability and the ability to produce pure d-fructose, suggesting its application to the production of high-fructose syrup.